History is not just what happens in time, it is how we we think about time. The present moment seems not just threatening but destabilizing because many of us are shifting from one sense of time to another. The concepts of eternity and inevitability conclude On Tyranny and frame "Road to Unfreedom." In this talk I explain them. Timothy Snyder is a historian at Yale University, specializing in eastern Europe, totalitarianism, and the Holocaust. His books have received widespread acclaim. His most recent book, "The Road to Unfreedom: Russia, Europe, America," tells the whole Russia story, from beginning to end, in a way that makes sense and reveals the big picture. He is also the author of "On Tyranny: Twenty Lessons from the Twentieth Century," which explores the everyday ways a citizen can resist the authoritarianism of today. His other works include "Black Earth: The Holocaust as History and Warning" and "Bloodlands: Europe Between Hitler and Stalin." Follow on Twitter: @TimothyDSnyder